Apparatus and method for improving the resolving power of analytical instruments



Oct. 27, 1964 B. R. F. KENDALI. 3,154,747

APPARATUS AND METHOD POE TMPROVTNG THE EESOEVTNG POWER OP ANALYTTCAL INSTRUMENTS /y mm? wmv/7% B. R. F. KENDALL 3,154,747 APPARATUS AND METHOD FOR TMPROVTNG THE REsoLvING Oct. 27, 1964 POWER OF ANALYTICAI.. INSTRUMENTS 7 Sheets-Sheet 2 Filed April 16, 1962 Oct. 27, 1964 B. R. F. KENDALL. 3,154,747

APPARATUS AND METHOD FOR IMPROVING THE REsoLvING POWER OF' ANALYTICAL. INSTRUMENTS 7 Sheets-Sheet 3 Filed April 16, 1962 um, @l A F M m F. KENDALL APPARATUS AND METHOD FOR IMPROVING THE RESOLVING Oct. 27, 1964 POWER OF ANALYTICAL INSTRUMENTS '7 Sheets-Sheet 4 Filed April 16, 1962 /57 fm ,We WL@ WM),

B. R. F. KENDALL 3,154,747 APPARATUS AND METHOD FOR IMFROVING THE RESOLVING Oct. 27, 1964 POWER OF ANALYTICAL INSTRUMENTS Y 7 Sheets-SheetI 5 Filed April 16, l 1962 im@ @W Oct. 27, 1964 B R, F, KENDALL 3,154,747

APPARATUS AND ME'HOD FOR IMPROVING THE RESOLVING POWER OF ANALYTICAL. INSTRUMENTS Filed April 16, 1962 '7 Sheets-Sheet 6 2,5% wyww wm Oct. 27, 1964 B. R. F. KENDALL 3,154,747

APPARATUS AND METHOD FOR IMPROVING THE RESOLVING POWER oF ANALYTICAL INSTRUMENTS Fiied April 1e, 1962 7 sheets-sheet '7 jah mmm L, i idf 107g; /A/fKPa/V// fffPa/w 5Fl/LCL@ /Z United States Patent O APPARATUS AND METHD FR MRGVENG TEE RESGLVNG PGWER F ANALYTECAL INSTRUMENTS Bruce R. F. Kendall, State College, Pa., assigner to National Research Council, Ottawa, Qntario, Canada, a corporation ol' Canada Filed Apr. 16, 1962, Ser. No. 137,567 Claims priority, application Canada Apr. 2S, 196i i4 Claims. (Cl. 32%-65) This invention relates to apparatus and method for increasing the resolving power of analytical instruments, and is particularly concerned with such apparatus and method when applied to that type of analytical instrument in which the output of the instrument may be presented as a spectrum consisting of variations in the magnitude of the response of the instrument against position along an ordhiate corresponding to the value oi some variable parameter related to a peculiar characteristic of the instrument input. Examples of this type of instrument are the mass spectrometer in which ion current is plotted against mass number (or more properly against massacharge ratio), and the optical spectrometer in which the luminosity of various parts of the spectrum is plotted against wave length.

ln an ideal analytical instrument the output is not capable of misinterpretation and presents a unique output component for each single input component. rhus, in the case of the mass spectrometer, the output should consist ot' a series of iniinitely sharp spectral peaks, each such peak being centered on, and only on, a given mass number, with the amplitude of the peak indicating the magnitude of the particular component associated with any given mass number.

However, due to compromises made in the design oi the instrument, constructional inaccuracies, and other factors, these ideal conditions are never met and the output response for each input component in fact becomes distributed over an appreciable range of values of the variable parameter, or in other words a response appears at values of the parameter where a response should properly only appear when other components are present in the instrument input, as well as the correc component. Up to a point this dispersion of the output of the analytical instrument can be tolerated since 'the results of the instrument can be interpreted notwithstanding its presence. However, when the overlap ot adjacent peaks resulting from this dispersion becomes appreciable the instrument ceases to present information which can be directly interpreted by the operator and for this reason it is customary to use analytical instruments only under conditions in which the overlapping or dispersion of the output information is negligible.

To avoid this overlap much work his been done in the development of increasingly more elaborate and costly apparatus of high resolving power, that is to increase he range of usefulness ot the instrument itself by making its output interpretable over a greater range.

It should be remembered however that even when the output of an analytical instrument is not directly interpretable, the basic information necessary ror such interpretation may still be present, and it is on this premise that the present invention is founded. rEhe fact that the information may be there but not directly interpretable has been appreciated by others and some attempts have been made to extract infomation from otherwise un- Lice interpretable spectra, particularly those made up of superimposed pealts. One know method of extracting useful information is the graphical method and this is often useful in mass spectrometry where a very small mass peak may be superimposed on the tail of a much larger mass peak. Here the only interaction to be allowed for is the contribution of the large peak to the indicated height or the small peak, and a method oi automatically stabilizing this contribution at a constant level while plotting the small peak has been previously proposed.

All of the known methods suffer from disadvantages in that they may be only applied to certain types of instruents and are frequently costly, tedious and time-consuming. rEhe present invention, while having iinite limitations as to the increase in resolving power which may be realized by its use, nevertheless can, tor relatively moderate cost, bring about a substantial increase in the resolving power of an analytical instrument and, as shall be shown later, is capable of widespread application. Moreover the output of the system disclosed in the present invention is either presented in the same form as that of the instrument itself, or alternatively provides the necessary data for the information to be presented in this form. l

The present invention is particularly useful with those analytical instruments in which the variable parameter ot the spectrum is restricted to integral numbers which may be made to correspond to xed positions along the spectrum. The invention is also especially convenient when the ordinal extent and formation characteristic ot the instrument response for a single component input are the same throughout the whole range of interest oi the variable parameter. Thus, as mentioned above, the present invention readily lends itself for use with a mass spectrometer, particularly when the deformation of the ideal output peak for a single input component is the same across the whole range of mass numbers under consideration.

In general terms, the technique of the present invention involves the operation of an electronic or other analog of an analytical instrument in coniunction with that instrument. Feedback paths are provided in such a way that the output spectrum of the analog device tends, by successive approximations, to become generally identical with the output spectrum ot the real instrument. When these output spectra are so related, the internally generated signals appearing at the input of the analog device, as required to set up or to maintain such identity, will in general correspond to the input of the real instrument. These internally generated signals can then be used to identity the components present at the input of the real instrument, and to obtain the relative amplitudes of those components. rl`his information can be displayed in the form of a spectrum in which tde component peaks are resolved.

More specifically, the invention in its broad concept provides apparatus for improving the resolution of an output received from an analytical instrument in which a sharply deiined input appears as a distributed output, comprising,

(a) Analog means for generating from a discrete input signal (analog input) an analog output in the same distributed orm as the instrument output,

- (b) Comparator for comparing the magnitude of a section of the analog output with the magnitude ot a corresponding section of the instrument output and for sensing a difference therebetween, and sections being narrow in'relation to the distributed width of said outputs,

(c) Input signal generator means connected to said comparator means and sensitive to a said difference for feeding an input signal to said analog means of a value to tend to bring said analog output towards equality of magnitude with said instrument output to nullify said difference (at least in magnitude-usually the signs are also equal, 'out they may be opposite),

(a) Means for carrying out a series of successive sweeps of both said outputs by said comparator means,

(e) And means connected to said input signal generator means for sensing the input signals to said analog means. Y

In operating the apparatus the sweeping means is caused toV sweep repeatedly while modification of the analog output is continued, whereby, by a series of successive approximations, the two outputs (instrument and analog) tend to become equal to each other.

Two basic alternatives are now possible.

Once the outputs have become equal, they can be allowed to remain that way (assuming no change in the instrument output). This condition of exact equality will mean that the output from the comparator means will disappear, since the latter senses only a difference between the instrument and analog outputs. The input signal generator means, which is sensitive to any difference detected by the comparator means, will then receive no input. In this case, the apparatus must contain some form of storage or memory if the analog means is to continue to provide the existing analog output. In this way a static condition can be reached, with all three signals, instrument output, analog input and analog output remaining unchanged (for each respective position of the sweeping means). Such static condition will remain indefinitely, or until the instrument output changes, when the system will readjust itself by bringing the analog output into agreement again with the new instrument output. This may be thought of as the separate storage method of constructing the system, because a storage determining the analog output must be provided which can'act without stimulation at the analog input. Y

The second alternative is not to allow the two outputs (instrument and analog) to maintain exact equality.

In arst sub-division of this second alternative, as the comparator means sweeps, it causes the input signal generator to feed a signal to the analog means that is reflected in the analog output in a way that achieves momentary equality between two narrow sections of the outputs which are atrthat time being compared by theV comparator means. But, as soon as the comparator Ymeans moves on to sweep the next sections of the instrument and analog outputs, the analog output begins to decay by an amount proportional to the dilierence between the value of the section in question and a respective reference level. With this manner of operation, an appreciable divergence between the instrument and theV cause it permits the analog output to be stored in the same device as the analog input, as will become clearer from the specific examples that follow. This arrangement :may therefore be conveniently referred to as the-fsingle storage decaying memory method of correction.V

Y A second sub-division ofthe .single storage. method-V namely a single storage, non-decaying memory method is also available. In this case the values of each section of the analog output are modified, but not by decay. They are each modified by an amount proportional to the difference between the value of the section in question and a respective reference level. The modification may be an increase or a decrease, and, since it will be applied by some external instrumentality (as distinct from a built-in decay), it may conveniently be applied to all sections of the analog output simultaneously during each interval between sweeps. The eiect is similar to that of the decaying arrangement.. Every time the comparator means sweeps, it iinds a dilerence between a pair of corresponding sections of the two outputs, and it acts to rectify this difference through the input signal generator. By the time it comes around again, the equality achieved during the previous sweep has been lost by virtue of the modication of the analog output.

In all these alternatives the sensing means which senses the input signals to the analog means supplied by the input signal generator provides an indication of the instrument input, and the object of the invention has been achieved.

Speciiic examples of manners in which the invention may be carried into actual practice will now be described in conjunction with the accompanying drawings, these examples being included by way of illustration and not of limitation. In these dram'ngs:

FIGURE l shows in simplified block diagram form the principal components utilized in the practice of the present invention;

FIGURE la is a diagram similar to FIGURE l illustrating the application of the system to a complex instrument output;

FIGURE 2 demonstrates the manner in which the present invention is useful in interpreting otherwise unusable output information from a mass spectrometer; FIGURE 2a showing the actual output of the mass spectrometer, and FIGURE 2b showing the same output when processed by the present invention to place its information in interpretable form;

VFIGURE 3 shows one form of the present invention for use with a mass spectrometer;

FIGURE 3a shows-a portion of a modified form of the circuit of FIGURE 3;

FIGURE 3b shows another manner of carrying the invention into practice;

FIGURE 4 shows a form of the present invention for use with an opticalspectrometer;

FIGURE 4a is a plan view of a fragment of FIGURE 4 on a larger scale;

FIGURE 5 shows the present invention When'applied to an analytical instrument whose output is a plot of luminosity against position in two dimensions;V

FIGURE 6 shows yet another embodiment of the invention, and f FIGURES 7a to 7c are diagramsillustrating the mauner of operation of the system of FIGURE 3. Y

The basic system of the present invention is shown in block diagram form in FIGURE 1. In this example there is assumed to be a single component input to theY analytical instrument. The case of a multiple coinponent fnput will be considered later With reference to FIGURE 1a. It will be seen that the output of the analytical instrument is shown in FIGURE l symbolically as a spectrum which, as mentioned above, may be generally considered as a plot of variations in the magnitude of the instrument response Yagainst position along an ordinate corresponding to the value of-a variable paraf meter related to a particular characteristic of theV instru-V V ment input,rfor example a plot of ion current against.VV mass number in the case of a mass spectrometer: In this output spectrum a known single component input to the analytical instrumentV should properly'be represented by a very narrow trace or peak S1 appearing only at that position along the spectrum of the particular value of the variable parameter which corresponds to the unique component. ln practice however it will be found that the output response for a single component input spreads over a tar wider range of values of the variable parameter occupying area S of the output spectrum and thus in eiect gives a response at values oi the variable parameter other than that corresponding to the known single component input. Thus for example if a substance of mass m is analyzed in a mass spectrometer, it should give a sharp response in the form of a narrow peak opposite mass number m on the output spectrum. lt is possible to design mass spectrometers to achieve this, but it would be preferable to use simpler equipment giving a peak centered on mass number m and dispersed over several adjacent mass numbers.

A fundamental part of the present invention is the provision of an analog device whose output consists oi a spectrum S3 of the same orm as that of the analytical instrument, and whose ordinal extent and formation characteristic are the same as those or section S of the instrument output spectrum. The analog device is so designed that the analog output spectrum S3 having the same ordinal extent and formation characteristic as that produced in section S of the instrument output spectrum for a single component input, is produced by presenting to the device an input whose ordinal extent and formation characteristic correspond generally to those which should appear in the output of the analytical instrument. Thus for the system shown in FEGURE l the analog output spectrum S3 is made to correspond as to ordinal extent and formation characteristic with S the actual secion of the instrument output spectrum associated with a single component input, and the analog produces this output spectrum S3 when presented with an input corresponding generally as to extent and formation with section S1, the desired instrument output spectrum.

The system thus far described enables the analog device to have an output spectrum S3 corresponding to area S of the instrument spectrum so tar as ordinal extent and formation characteristic are concerned, but there still remains the necessity of ensuring that the magnitude or intensity of the analog spectrum S3 corresponds to that of area S, and this is done by comparing the magnitude or intensity of a narrow` central section of the area S, which may conveniently be the section Sl, with a centrally located section S2 or" the analog output spectrum, such section S2 being conveniently of the same ordinal extent as section Sl.. Then, by feedback techniques, the mean amplitude of section S2 is made equal to that of section Sl. As will be shown later this comparison may either be done directly so as to make the magnitude or intensity of the analog output strip S2. equal to that of strip Sl of the instrument output spectrum, or alternatively the magnitude oi strips Sl and S2 may be made equal and opposite in sign in relation to a reference level (for purposes explained below).

It will be seen that from the comparator in which the comparison of the two strip intensities is eected the resultant dierence signal is applied to an input signal generator which in turn has its output applied as the input to the analog device.

Thus, as has been explained, the analog device has an output spectrum S3 of ordinal extent, formation characteristic, and magnitude corresponding to those of section S, which is that section oi the instrument output spectrum associated with a single component input, and produces this output spectrum from an input of narrow extent generally equal to that of strip Sl.. Under these conditions the input to the analog device has an extent, formation and magnitude corresponding to those of strip Sl, which is of course the output response the analytical instrument should give for arsingle component input,

when in practice it gives an output response corresponding to section S. It the input to the analog device is now examined in a system output display then the output from the system will be observed as a response of ordinal extent, formation characteristic, and magnitude corresponding to those oi strip Sl which means that the analog system has produced an loutput corresponding to the desired output from the analytical instrument as opposed to the actual output from the analytical instrument which has suilered from distortion.

Thus far, of course, the only comparison which has been effected has been when the analytical instrument is presented with a single component input of known position along the variable parameter, and in practice the instrument input will be a composite one rather than a single one, and the output spectrum will consist of many such individual output sections distributed along the variable parameter. Accordingly it is necessary to cause the comparator to scan repeatedly along the analog spectrum and along the instrument spectrum matching them at successive points, and this is done by electrical, mechanical or optical means, as the case may be.

FlGURE 1a illustrates the basic system similarly to FlGURE l but for composite (spectral) outputs from the analytical instrument, in place ot the single output assumed in FIGURE 1. FIGURE la shows the same essential components, namely analytical instrument, comparator, input signal generator, analog device and system output display. In addition this system includes a sweep-synchronizer which controls scanning by the comparator of both spectra and synchronises such scanning with the sweep of the system output display. This ligure shows a composite instrument output spectrum S4 which is made up oi a number oi superimposed spectra S. In the same way the analog spectrum S5 is made up of a number of superimposed analog outputs S3. The scanning of the analog spectrum is of course synchronized with the presentation on the system output display so that the system output is displayed once for each scan.

As was stated above, the analog output S3 (FIGURE l) is made to have the same ordinal extent and formation characteristic as those of that section S of the instrument output spectrum corresponding to a single component input to the instrument. Provided the distortion introduced in the instrument is constant, i.e. the extent and formation of section S is the same throughout the Whole of the instrument output spectrum, or at least throughout that range of the variable parameter which is of interest, then the extent and formation of section S3, i.e. the analog output, need not vary with the position of section S'along the instrument output spectrum, and the present invention is most useful where this generalization holds true. However the system can be used even when the extent and formation of section S varies with its position along the instrument output spectrum and this may be done in the system of FIGURE la by feeding the output of the sweep synchronizer additionally to the analog device itself so that the extent and formation of the analog output can be made to vary in accordance with the position of the scan along the instrument output spectrum. To determine how the extent and formation of the analog output shouldvvary with the position of the scan, it is best to apply single component inputs to the analytical instrument for diiierent values of the variable parameter distributed throughout that range of the instrument Voutput spectrum which isoi'f interest. This enables the analog output to be calibrated, as it were, along the whole range of interest of the instrument output spectrum.

The results realizable with the foregoing system employing a double component input tothe analyticalinstrument may be best appreciated from a study of FIGURE 2. FGURE 2a shows the output spectrum obtained from a mass spectrometer when two isotopes of argon, namely argon 4t) and argon 33 were applied to its input in the ratio of approximately 4.3 to 1. FGURE 2b shows the system output display when the present invention was' applied to this same mass spectrometer, and shows how effectively the resolving power of an instrument may be improved by the present invention.

The system which produced the results shown in FIG- URE 2b is shown in FIGURE 3, and a detailed description. of this system will give a better understanding of the present invention. This system is of the ,single storage, decaying memory type described above. The analytical instrument whose resolving power is to be improved is a mass spectrometer 2 having a collector 21 which, as the output of the mass spectrometer is swept across the collector by the sweep circuit 2a controlled by the sweep generator 5, is struck i1 succession by those ions having a progressively higher common mass per unit charge. The sweep generator also controls via link 32 the position of the rotary arm 31 of a rotary switch 3. This rotary switch has a large number of contacts 30a, 30b 30u 30x, which the wiper arm 31 thus sweeps in synchronism with the sweep generator 5. The speed of rotation of switch 3 is normally made appreciably faster than that of the analog output scanning system, which will be described later, but can approximate this speed if the decay time is made long.

The output of the collector 21 is applied via ion current amplier 4 to rotary wiper arm 31 so that, due to the synchronism of the system, the wiper arm repeatedly donates to each switch contact a current proportional to the amount of ion current reaching collector 21 while the arm is on that contact. Thus, for example, contact 3011 will always receive a current corresponding to the number of ions impinging on collector 21 when the mass spectrometer is sweeping through mass number n. If the spectrometer had an ideal output response, current would be donated to one switch contact only, when a gas of unique mass number was' analysed in the mass spectrometer, but in practice it may be found that currents are donated to at least one, and generally to two or more, of the switch contacts on each side of the switch contact corresponding to the particular mass number of the component input being analyzed.

. The current from each switch contact is fed separately to one of an associated series of resistors and capacitors connected in parallel Yto a common reference potential, which may be suitably` ground potential. Thus current donated to contactr30a is fed by terminal 10a to capacitor Ca' connected in parallel with resistor Ra', the other side of the parallel RC circuit being connected to ground. Suticient switchY contacts and associated parallel resistorcapacitor combinations are provided Vto cover all of the integral mass' numbers falling within the range of interest, and thisV isillustrated .symbolically by the fact that the switch contacts go as high as 30x connectedtto ground in series with capacitor Cx' and resistory Rx' in parallel.

For the general case, switch contact 3011 associatedwith mass number n is connected via terminal 1011 to capacitor Cn', ,which isv parallel connected with resistor Rn', the (other sides of these components being connected to ground.Y Contacts 3011-1 and 30114-1, associated with massnurnbers n-1 and Vn-l-l respectively, on each side of contact30n are connected in similar fashion to capacitors Cn-1, Cn{-l, via leadsj 101171 and 10i/t+1. Thus each vtime rotary wiper arm 31KV Ysweeps acrossthe switch contacts'tla 3011 301e, associated capacitors Ca' Cn' t Cx Vreceive a charge corresponding to the number of ions reaching the collectorAZl while'rthe 'arm 31V is on the respective switch contacts, and thus the v each capaictor provides a discharge path of long time constant so that a small portion of the Vcharge in veach capacitor leaks away between successive" wipes. of the rotary arm 31, thus enabling the capacitors to continuously represent in close approximation the correct output spectrum for the mass spectrometer.

In the event that it is desired to analyse existing records, the inputs to the remainder of the circuit, which the charges on capacitors Ca Cn' Cx represent, can be provided by a series of potential dividers manually set to give potentials corresponding to the ordinates of vthe recorded spectra (that is prerecorded instrument output) at successive mass numbers.

Each switch contact 30a .y 30u 30x is also connected to one side of another parallel RC circuit consisting of capacitors Ca Cn Cx in parallel with resistors Ra Rn Rx, the other side of each of these RC combinations being connected respectively to contacts 60a 601i 60x of a rotary switch 6.

This rotary switch 6 may have three wiper arms W1, W2 and W3 which may be considered connected at any instant to switch contacts 601i, 6011-1 and 60114-1 respectively, i.e., the wiper arms are arranged to be one contact out of phase with each other. Wiper arms W1, W2 and W3 are connected via variable'resistors R1, R2, R3 respectively to a common junction 12, and wiper arm W1 is also connected via an amplier 9, to this junction 12. Amplitier 9 is a direct current amplifier of large gain having reversed polarity between input and output. As will be explained later, it is advantageous to include between amplifier 9 and junction 12 a diode D1, with a resistor RD1 between junction 12 and ground, though the presence of the diode D1 is not essential if only a low increase in resolving power is to be attempted. In addition, it is also convenient to provide a diode D2 with series resistor RDZ between the output of amplifier 9 and wiper arm W1. The direction of the diodes D1, D2 has been shown as suitable for the example which follows, in which it is assumed that negative potentials are applied to terminals 10a 10x. If positive potentials were applied at these terminals, the direction of both diodes would be reversed.

As was mentioned earlier, the mass spectrometer when analysing a single component input does not give a'unique output ion current at the appropriate mass number but rather gives a distributed output response centered on the particular mass number but having, in addition to the ion current at the proper mass number, ion currents present at at least those mass numbers immediately adjacent the particular mass numberV and frequently for two or more mass numbers on each side of the given mass number. The operation of the system may-be best understood by 1magm1ng that, for the moment, a single component input of mass number n is being analyzed by the spectrometer and that this input is giving a distributed'output response centered on rotary contact 3011 of rotary switch 3 such that capacitor Cu? has formed thereon a charge proporltional to the ion current appearing at the collector when the spectrometer is sweepingV through mass number n as islproper, but also capacitor Cn- 1, Cn'-{1 have received charges even though-there are no input components Ato the mass spectrometerthaving mass knumbers n-l, or n+1. It is, of course, this charge dispersion which the present system seeks to eliminate or at least substantially reduce.

Before the rotary switch 6 begins to sweep,'the storedy charge on .capacitors Cn'-l, Cn and C11-H will set-up corresponding potentials with respect to ground on contacts 6011-1, 6011 and 60n-1-1. Whenvthe wiper arms W1 to W3 begin toV sweep around the rotary switch, these potentials will be detected by arm'Wl, amplified and changed insign by ampliiier 9 and returned via junction 12 to arms W1, W2 and W3 to charge up capacitors C11-l,V Cn and Cn-i-l to potentials tending to balance-the potentials on capacitors C11 -l,A Cn and Cn'i-{V-l. It requires a number of sweeps `to set up an equilibrium condition, a fact best illustrated by numerical examples.V The 9 rst example to be given will assume a single component input, as above indicated.

Suppose the ordinates of the single peak representing mass 11 are in ratio 0:1:2:0 at mass numbers 11-2, 11-1, 11, 1i+2 respectively. The pattern of currents fed by the wiper arms W2, W1 and W3 is made to be in the ratio 1:2:1 by adjustment of the relative values of resistors R2, R1, R3. Suppose that when switch 6 begins its rst sweep there are potentials 0, 100, 200, 100, arbitrary units on terminals 1011-2, -1, 1011, 1011+1, 1011+2. For simplicity it is assumed that the wiper arms move across the contacts 6011-2 6011+2 in a time which is' short compared with the time between successive sweeps. r[he potentials on 6011-2 6011+2 will be the same until the center wiper arm W1 reaches Contact What has happened is that on detecting the 100 potential on contact 6011-1, the amplifier 9 has delivered a positive output (analog input) which passes through resistor R1 and restores the potential on arm W1 and contact 6011-1 to ground potential, a charge being stored in capacitor C11-1 equal and opposite to that in capacitor C11 1. The resistors R2 and R3 are each set to have twice the value of resistor R1, and therefore charges of +50 units will be simultaneously transmitted to contacts 6011-2 and 6011 modifying their voltages as above indicated.

Now, when the rotary switch 6 steps forward one contact, the detecting arm W1 reads the 150 potential on contact 6011, restores this and adds +75 units to the two contacts on each side. This action and that of the suctact 6011+2, receives a positive potential. This generates a negative output from amplifier 9 which is blocked by diode D1, but passed by diode D2 to the arm W1, but only to arm W1. No output appears at junction 12, so no output appears on the oscilloscope S, and the adjacent arms W2 and W3 pass no current.

The potentials of the last row above are thus those remaining between the contacts concerned and ground when the wiper arm W1 passes beyond the area of interest.

Before the next sweep of the rotary switch 6, these potentials will be modied by decay through resistors R11-2 R11+2. They will each decay by an amount proportional to the potential difference between each contact 60 and its corresponding terminal 10 (the latter still being charged at the original pattern, since it is assumed that there has been no change to input conditions). Assuming the proportion of deca which proportion will be the same for each section under consideration (eg. each Contact), to be 1%, the potentials remaining after the decay time will be 6011-2Z50-l% of 50=49.5 6011 l:75 1% of175=73.25 6011:12.5 1% of 212.5:10375 6011+1:0 1% of 100:-1 6011+2:0 1% of 0:0

10 If now these are the potentials presented to the wiper arms when they made the second sweep, the result will be as follows:

Note again that the majority of outputs from amplifier 9 were negative and consequently of no etect on the adjacent wiper arms.

Two sweeps have now taken place, and a potential remains only on contact 6011. With the same 1% potential change between sweeps the results of the third, fourth, iifth and sixth sweeps will be approximately as follows:

Potential on- Arm W1 on- CTIJiii-itlslt passed by 60n-2 6011-1 60u 60n+1 6-lu-I-2 arm W1 Third Sweep:

50n- 0 1. 00 1. 5. 1. 00 0 0 6011-2 0 1. G0 1. 50 1. 00 0 0 60m-1 +0. 50 0 1. 00 1. 00 0 1. 00 Gun. +0.50 +0. 50 0 0. 50 0 1. 00 6in1-+1. +0. 50 +0. 50 +0. 25 0 +0. 25 0. 50 60r1+2 AA +0. 50 +0.50 +0. 25 0 0 0. 25 Fourth Sweep:

. 1. 88 1. 00 0 0 6fm-2.-" 0 0.25 1.88 1.00 0 0.25 GDH-L +0.12 0 1.76 1.00 0 0.25 +0.12 +0. 8S 0 0.12 0 1.76 +0. 12 +0. S8 +0. 06 0 +0. 06 0. 12 +0. 12 +0. 88 +0. 06 0 0 0. 05

0.12 0.12 1. 94 1. 00 0 0 0 0. l2 1. 95 1. 00 0 0. 12 60n 1 +0. C6 0 1.88 1.00 0 0.12 60u +0. 06 +0. 94 0 0. 06 0 1. 88 50u-+1.. +0. 05 +0. 94 +0. 03 0 +0. 03 0. 06 60n+2 +0. 0S +0. 94 +0, 03 0 0 0. 03

Potentials are only accurate to i001 unit from the third sweep on. The potential fall between sweeps (compare the last line of the fth sweep with the first line of the sir-ith sweep) has now become approximately 0, 1, 2, 1, 0 units respectively. lt will be observed that this fall (modification of the sections of the analog output) is in the case of each section proportional to the difference between the amplitude of such section of the analog output and a reference level.

At each successive sweep, the current passed by the center wiper arm W1 is approaching zero for al1 positions except when this arm is on contact 6011. 1n this position the current passed by the arm is tending towards +2 units. This figure represents the amount of charge lost by capacitor C11 between each sweep. It represents a potential of 2 100 units on terminal 1011. The oscilloscope display 3 would therefore be approaching an indication of a single peak of mass 11 and of amplitude 2X 100:200 arbitrary units. Such a display corresponds to that which could be obtained from the output of a mass spectrometer capable of completely resolving the adjacent masses. It may also be noted that the potentials on 6011-2 6011+2 tend towardsO, 0, 2, 1, 0 at the start of a sweep, changing to 0, +1, 0, 0, 0 after the center wiper arm has passed 6011. During the interval between sweeps these potentials decrease by 0, 1, 2, 1, 0

y3,155,74ri

`units respectively, to again give 0, 0, 2, 1, 0 at the start of the next sweep.

These potential changes which result from the method of successive approximations may conveniently be illusl2 that is the interval between successive sweeps. It will be observed that due to the stored potentials on capacitors C11-2 to Clt-+2, both curves P2 and P3 are returning from their FIGURE 7b conditions towards their FIGURE trated graphically in the manner of FIGURES 7a, b and 5 7a conditions, which latter are the beginning of the next -c, which show the variations with time, after the system sweep. Y has reached a stable condition, of the potentials on ter- Consider now the situation when the instrument input VIninals 60 for a single component input of simple triis complex. Iangniar distributed forni, CUI'Ve P1- Suppose that the ordinates of a single peak are again Curve P1 represents the Potentials 0n terminals 1011-2 10 in the ratio 0:l':2:1:0 for successive mass numbers. The 't0 10H-P2 (instrument Output spectrum); Curve P2 TSP' current pattern fed by the wiper arms will again be in the resents the potential differences across capacitors C11-2 Same rati@ Suppose that a Complex peak is to be t0 CYL-t2 (anaiog Output Spectrum); CUrVS P3 represents analysed and that this is made up of two components, .tasturias551102025310Sa ed gaat ai 15 @am@meterte D i in e ratio uppose t att e arger pea as or 1- VP4, part 0f Winch is comcldent Wlth part of curve PZfrepnat-es of 0, 100, 20o, 100, 0 at mass numbers n 2 .Tesrts vlfgfltggzetlcare idealised in that n-{2 respecigelf, and that thebsmaller peak has ordinates s A 0, 50, 100, at mass num ers n- 114-3 respecgewnllllnlg rfugirpsn SS ciltills lmvri 20 tively. The complex peak would thgn have ordinates of 0, 100, 250, 200, 50, 0 at as num er -2 3 assumed to be in an early part of the sweep across conm s s n H+ respectively. Suppose the system is switched on with cortacts 60n 2 to 60n+2 in FIGURE 7a. Trace T demonresponding negative potentials on terminals 10ft-2 strates the trace on oscilloscope 8 (system output dis- 0 3 I h th play). At this position the instrument and analog out- 1 H+ 651s azssumed at 3 wlpef armshfngv? acoss puts are equal, so arm W1 detects nothing and there is no 25 Contacts t l. a um? W 1c 1s s Uff deecton of trace T compared With ghe time betwelei successive sweeps. It is FIGURE 7b shows the conditions immediately after Igaulasumd tlat the mtev] eltlween Succsswe Sweps arm W1 has reached the center contact 60n. Contact 60n ls'su Clem or percent 0 e c arges on t e capacitors has been brought to ground potential, the charges passing C t0 leakaway. The potentials on contacts .6011-2 to contacts 6011-1 and 6011-i-l bringing the curves P2 30 .60'i3 Wm be the Same as thfse on terminals .10H-2 and P3 to the new shapes shown. The current units 10ft-b3 Until the Center Wiper arm reaches Contact passed by arm W1 (analog input) appear as a peak T1 6011-1. Thereafter, the potentials on 60n-2 6011 on the trace T. The potential on contact 60n+l has now +3 and the charges passing through the center wiper will been brought to ground, and so the sweep continues withbe as follows:

Potentials on- Current units Arm Wl onpassed 60n 2 60n 1 60u 5011-1-1 00n+2 60n+3 bywm First Sweep:

60n 2 0 100 250 200 50 0 o +50 o 200 200 50 0 100 +50 +100 0 100 50 0 200 +50 +100 +50 0 o 100 +50 +100 +50 0 0 0 0 Senond Sweep +50 +100 +50 0 0 0 0 60m-al +495 +98 +47 2 0.5 0 0 0 0 +47 2 0.5 0 es 0 0 0 2 0.5 0 47 0 0 +1 0 +05 0 2 0 0 +1 0 0 0 0.5 0 0 +1 0 0 Y 0 e 0 out any further passage of current through the wiper arms or any further deflection of trace T.

FIGURE 7c shows the corresponding distribution of potentials after elapse of half the decay time interval,

Potentials are only accurate to 10.01 unit from the third sweep on. The potentialtfall between sweeps has now become approximately O, 1, 2.5, 2, 0.5, 0 units respectively.

Potentials on- Current units Arm Wl 011- passed 6011-2 6013-1 60u 'o`0n-l-1 60n+2 00u +3 bymam Fifth Sweep:

0. 25 1.88 2.00 0.50 0 0.25 0 1.76 2.00 0. 50 D 0.25 +0. 88 O 1. 12 0.50 0 1. 76 +0. 88 -l-O. 56 0 +0. 06 0 1.12 -I-D. 88 +0. 55 0 0 0 0. 06 +0. 8S +0. 56 0 0 U 0 0.12 1. 94 2. 00 0.50 0 0 0. 12 1. 94 2. 00 0. 50 0 0. 12 O 1. 88 2. 00 0. 50 0 0. 12 +0.91 0 1.06 0.50 0 1.33 +0. 94 +0. 53 0 -l-O. 03 0 1. 0S +0. 94 +0. 53 O 0 O 0. 03 6011 --0. 06 +0. 94 +0. 53 O 0 0 0 Seventh Sweep 6in1-3l +0. 06 0. U6 1. 97 2. 00 0. 50 0 0 6011-2 0 0. O6 1. 97 2. 00 0. 50 O 0. O6 0 1.97 2. G0 0.50 0 0.06 +0. 97 0 1. 03 0.50 0 1. 94 -l-l). 97 +0. 51 0 +0. 01 0 l. 03 +0. 97 +0. 51 0 0 0 0. 0l +0. 97 +0. 51 o o o o At each successive sweep, the current passed by the center wiper arm W1, the analog input, is approaching zero for all positions except when this arm is on contacts n or n-I-l. In these positions the current is converging towards +2 and +1 units respectively. As before, these signals represent resolved mass peaks of masses n and n+1 and having amplitudes or" 200 and 100 arbitrary units respectively. This analog input spectrum appears at the oscilloscope 8 which constitutes the system output display and shows the mass spectrum which could have been obtained using a mass spectrometer capable of completely resolving the adjacent peaks. Sweeping of the oscilloscope 8 is synchronised with that of rotary switch d by sweep generator 7, as indicated symbolically at 62. Vfhen the system is started from rest the oscilloscope display normally reaches a steady state after iive to ten sweeps of the wiper arms so that, in one system where tile revolution rate Was one cycle per second, the display reached a steady state after iive to ten seconds.

It can be shown that the speciiic system of FIGURE 3 is properly represented by the general layouts of FlG- URES l and la. The instrument output spectrum may be considered as the charges in the series of capacitors Ca Cn' Cx', each associated with a different ms number, and extending across the entire range of interest, which capacitors charge up in direct proportion to the ion currents present at the output of the mass spectrometer when the respective mass numbers are selected. These capacitors reiiect `the distortion in the output of the spectrometer in that a single input cornponent charges up not only that capacitor properly associated with its mass number, but in `addition charges the surrounding capacitors associated with adjacent mass numbers. Thus, in elect, section S of FGURE l is represented by the number or" capacitors which receive ion currents when a single component input is presented to the mass spectrometer, and strip Sl is represented by that capacitor associated with the mass number corresponding to the single component. The analog output is represented by the charges on capacitors C41 Cn Cx built up by the wiper arms which have their current pattern so arranged, by adjustment of their associated resistances Rl to R3, as to tend to build up charges on capacitors Ca Cn Cx to neutralize the charges on the instrument output spectrum capacitors.

Continuing the consideration of the relationship oetween FIGURES l and la, on the one hand, and FIG- Uli?. 3 on the other, the amplifier 9 and diodes Dl and E2 can be considered `as providing the input signal gener'ator, while the amplifier 9 also functions along with the center wiper arm W1 as the comparator. The analog device may be considered as represented by the three resistances Ri to R3, the rotary switch 6 including contacts 60a 6011 60x, and the analog storage capacitors Ca Cn Cx. Resistors Re Rn Rx function as means for modifying all sections of the analog output (as stored on capacitors Ca Cn Cx), by providing for decay of the capacitor potentials. The current units passed by wiper arm W1 represent the analog input spectrum.

n the present case three Wiper arms have been shown but in practice tive, seven, or more wiper arms could be used to get even closer approximations to the desired result. r'nere only remains the comparison of the magnitude `of the two output sections and this is done indirectly, in the manner referred to earlier in connection with FIGURE l, by comparing the instantaneous voltage on wiper arm Wl (which may thus be considered the same as the narrow strip S2 of FIGURE l) with a reference voltage, in this case ground potential, so that there flows through Wiper arm W1, a charge suicient (and of correct sign) to change capacitors Ca Cn Cx to potentials equal land opposite to the potentials on respective capacitors Ca Cn Cx.

The degree of improvement in resolving power depends on the number of wiper arms used. With a simple system such as that shown in FGURE 3 the resolving power of a mass spectrometer could be made approximately four times as great, i.e. this system has a multiplication factor of 4. In a more complex system with seven wiper arms and 26 contacts on switch 6, a resolving power multiplication factor of 8 has been obtained.

To accommodate the situation which arises when the analog output must vary as to ordinal extent and formation characteristic throughout its scanning cycle, it is or course necessary to vary the values of resistors Rl, R2, 3 etc. (depending on the number of wiper arrns used) as the analog output goes through its scancycle, with some of these resistors possibly becoming infinite, i.e. Vopen circuit, when the ordinal extent is to be reduced. ln practice lthis result can be achieved quite readily by constructing switch e as a commercial stepping switch of the type known as a Strowger switch in the telephone art, in which the wiper arms do not successively scan one Yset of switch contacts but rather each wiper arm has its own set of associated switch contacts,

i.e. there are .as many sets of switch contacts as therev are wiper arms. Thus each wiper arm has its own switch Contact for each mass number and a resistor of the appropriate value for the wiper arm and switch contact under consideration can be inserted in the contactY connection. Oi course many more resistors are used, and thus the simpler system is normally-used wherever possible, but nevertheless variations in the analog output 15 response both as to lateral extent and formation characteristics can be 'accommodated if desired.

In the system of FIGURE 3, the amplitudes of the various sections of the analog output, as stored on capacitors Ca Cn Cx, are modified between sweeps of switch 62 by decay of the potentials on such capacitors through resistors Ra Rn stants are such as to permit only a small percentage decay in the period between sweeps, and all the decays take place in the same proportion (for example 1%) of the initial potential. Since these decays are proportional to the potentials on capacitors Ca C11 Cx, and the potentials on these capacitors have been built up to balance the potentials on capacitors Ca Cn Cx', the decays are proportional to the potentials `on the latter capacitors, which potentials represent the instrument output.

It is this latter proportionality that is the truly fundamental one, a consideration which will facilitate appreciation of the modified circuit illustrated in FIGURE 3a which lis of the single storage, non-decaying memory type, above referred to. FIGURE 3a shows only a part of FIGURE 3, the parts not shown being the same as in FIGURES. The modification consists of eliminating resistors Ra R11 Rx (thus eliminating the decay paths); disconnecting from terminals 10a 1011 10x the terminals of capacitors Ca Cn Cx on the sides remote from terminals 60a 6011 60x and connecting such capacitor terminals to ground; and providing a multipole switch 63, each pole of whichV is arranged when the switch is closed to connect terminals 60a 6011 60x to respective terminals 10a lOn 10x each through a servo amplifier 64. The purpose of these connections is to modify the potentials on capacitors Ca Cn Cx (analog output) by amounts proportional to the potentials on lcapacitors Ca' C11' Cx' (instrument output). Servo ampliiiers are best suited to this function, as it is necessary that the increments of potential added to 'or subtracted from the analog output sections should be truly proportional to the potentials of the corresponding instrument output sections regardless of the existing potentials on the analog output sections and with a minimum of disturbance to the instrument output itself. Control `of switchV 63 is exercised by the sweep generator to ensure that switch 63 closes in each interval between sweeps of switch 62.

Applying this circuit to the simple numerical example given above, where potentials of 0, 100, 200, 100, units were assumed to form the instrument output on terminals n 2, 1011-1, 1011, 10114-1 and 10114-2, the

Y potentials on the corresponding terminals 6011-2, 6011-1,

6011, `60714-1 and 60114-2 will fall by 0, 1, .2, 1, 0 units when switch 63 closes between sweeps, assuming 1% of the potentialsare transferred. Operation of this 'modified system is thus very similar to that of FIGURE 3, except that the potential drops between sweeps will be constant from the first sweep, instead of only'approaching 0, 1, 2, 1, 0 units after several sweeps by successive approximations.

Consideration will now be given to the separate storage aspect of the present invention. In this'case, essentially the same basic circuit as that of FIGURE la is employed, except that the input signal generator employs a separate memory on which is built up a store of the analog input as this is generated, this stored analog input spectrum being modified in successive sweeps until the 'Y analog output spectrum becomes identical with the instrument output spectrum. Until the instrument output spectrum varies, the system remains static,since there is no inter-sweep modication'of the analog output spectrum. The storedwanalog input spectrum can then bereadV out fat will into the system output display. Y

' A numerical example will again be taken to facilitate understanding'of'the system, and, as'before'a simple,

. Rx. The time con- First peak 0 100 200 10G 0 0 Second peak 0 0 50 100 50 0 IOS 0 100 250 200 50 0 initially the analog input spectrum (AIS) and the analog output spectrum (AGS) will be zero. Now the comparator measures the difference IOS AOS which initially stands at the same as the IOS, namely In step 1 of sweep 1the comparator detects the first (left hand) of these values, namely 0, and there is no effect.

in step 2 of sweep 1, the comparator detects the second of these values, namely 100, and stimulates the input generator to feed a corresponding signal of 4-100 units as this section of the AIS, which now overall appears as belows:

The analog device spreads this signal in imitation of the characteristics of the analytical instrument, so that the AOS has added to it the values:

Thus the AOS in total becomes:

since it was entirely zero before this step. The values of IOS-AOS are now:

since the IOS is assumed constant throughout.

In step 3 of sweep 1, the comparator now detects the third of these values, namely 4-200. As a result the AIS becomes:

and the AGS has added to it:

to become:

Now 10S AOS has become:

In step 4 of sweep 1, the comparator detects the fourth of these values, namely 4-100. As a result the AIS becomes:

and the AOS has added to it:

0 0 4-50 Y4-100 4-50 0rV to become:

ln consequence VIGS-16193 becomes:

Y In stepsV 5 and 6 of sweep 1` no further changes take place` Y because in each case the comparator reads a zerorvalue for IOS-AOS. These V.valuesrthus persist until the second sweep, since there Visno inter-sweepYnioditication'of A potentials;

and the AOS has added to it:

making AOS:

It will now be seen that IOS-AOS has become:

and the sought identity between the instrument and the analog outputs has been achieved. From henceforth the system remains static until the IOS varies, since the comparator continues to detect zero on each step of each sweep.

It will be noted that simultaneously with achievement of this equality between the outputs, the AlS has become:

which will be seen to represent the two instrument output peaks, fully resolved and of correct amplitude.

Apparatus functioning in this manner is ilustrated in lGURE 3b, and comprises three synchronously driven loops of electrostatic storage tapes 71, 72 and 73, tape '7l acting to store the instrument output spectrum applied to it by read-on head 74, and tape 72 acting to store the analog output spectrum and as part of the analog device. Read-out heads 75 and 76 feed corresponding sections or" these two spectra to the comparator 77, in accordance with the general case illustrated in PEGURE la. The input signal generator 73 to which the comparator 77 is connected will be an mpliiier, it" gain is needed, although in this form of the invention it may comprise simply a wire for transferring the output of the comparator to the next elements of the system.

Maintaining the adherence of the circuit to the general structure of the invention illustrated in FlGURE la, the input signal generator 73 feeds to two places: the system output display and the analog device.

The system output display consists, in this case, of tape 73 which receives every output from the input signal generator through read-in head 79, and, during successive sweeps (that is successive rotations oi tape 73), integrates these signals to provide a record of the aggregate of the output of the input signal generator, which is equivalent to saying the aggregate of the analog input. ri`his stored information (analog input storage) is displayed on oscilloscope 30 by means of read-out head 8l.

The analog input from the input signal generator is applied to a standard peak shape storage 82 and the signal so received is used to modulate the intensity of a signal fed by storage S2 to an oscillating read-on head 33. This head E3 builds up the analog output spectrum on the tape 72. until it becomes equal in value and distributed form to the instrument output spectrum (this being the static condition iinally reached in the immediately preceding numerical example), when the output from the comparator 77 and the input signal generator 78 has become zero in all positions around the tapes. The analog input storage on tape 73 will have achieved a static condition by this time, such condition being truly representative of a esolved instrument output and which will be displaced in oscilloscope S0. To achieve the distributed form of analog output spectrum necesary to correspond to the unresolved instrument output spectrum, the readon head 83 is oscillated back and forth along the tape 72 as indicated by arrows 84. This oscillation will have a period several orders of magnitude shorter than the period of tape rotation determined by drive shaft 85. The range of oscillation of head 83 will correspond to the distributed Width of an isolated spectral peak, and as head 83 oscillates, the eiiective resistance in series with the head will bervaried in the storage 82 (eg. by a potentiometer driven by a suitable shaped cam) so that the average charge pattern transferred to tape 72 corresponds to the distributed shape of a spectrum peak, the magnitude of such peak being determined by the amplitude of the signal received from input signal generator 7S. If a cam is used to vary the resistance, its shape represents the stored standard peak shape (if head 33 moves at a constant speed).

Conveniently the read-on heads may take the form of small rollers touching the surfaces of the tapes and connected to high impedance outputs to allow read-on without loss of the signals already stored on the tapes. The read-out heads may similarly consist of small rollers connected to high impedance inputs.

A negative rejection circuit 86 also receives the signal from readout head 3l. Whenever the head 81 detects a slightly negative potential appearing on tape 73, indicating a tendency for an analog input peak of negativ-e amplitude to be recorded, the negative rejection circuit 86 will temporarily hold the output of the comparator 77 to zero. This circuit 86 avoids any tendency to instability and reduces the time taken for the system to come to equilibrium.

in the systems so far described the output spectrum of the mass spectrometer was in etiect displayed either in the form of variations in the state of discrete elements such as the charges on a series of capacitors, with each capacitor corresponding to a sequentially higher mass number, or in the form of a spectrum of charges along electrostatic storage tapes. The instrument output could quite conveniently have been displayed in other forms. One method of doing this is to display the output in the form of luminous intensity variation along an elongated trace corresponding to variations in mass number. This can be done by moving an intensity-modulated spot linearly over a photo-persistent surface (or similarly by synchronously moving the intensity-modulated electron beam of an oscilloscope). ln this condition the output of the mass spectrometer is in the same form as that of the optical spectrometer shown in FlGURE 4.

Here the optical spectrometer 102 feeds its output to a light source ldd in a housing 107 in whose front face is formed a slit 10S so that variations in the light output of the bulb M55 fall on the photopersistent surface lill of the upper section A of revolving drum 100. Drum is rotated by means of shaft 103 connected to drive motor 104. Sweep synchronizer controls the rotation both of drive motor 104 and the presentation of the output or optical spectrometer a02 so that the ouf.- put of the spectrometer is repetitively and synchronously displayed in the form of a spectrum on upper surface A. This spectrum consists oi variations in the intensity of the trace against position around the drum, wmch position corresponds to wavelength (or in the case of the mass spectrometer to mass number).

Ideally the output of the spectrometer should have the form of trace t, i.e. the variation in intensity should have only a very limited ordinal extent, but in practice the output will have the form of trace t1, ie. vili be distribn uted over an appreciable ordinal extent and will have a definite formation characteristic as to intensity variations over this extent. rihus in erlect trace is the ic al output and corresponds to strip Si of FIGURE l, ann trace t1 19` is the practical output for a unique component input and corresponds to strip S of FIGURE l.

In the system shown in FIGURE 4 the analog device has the form of an optical projector comprising an elongated light-tight housing 113 in which are positioned lenses 114 and 116, and between them a transparency 115. Illumination is provided by light source 112. Transparency 115 is so designed that the analog output as projected on lower surface B of revolving drum 100 has the same lateral extent and formation characteristic as does trace r1, and this is shown as trace l2 on lower surface B. Transparency 115 may either be obtained by appropriately marking a transparent piece of material, or alternatively it can be a photographic positive transparency produced from trace t1.

With this arrangement the output trace t2 of the analog device is the same as to ordinal extent and formation characteristic as that of trace t1 of the instrument output section associated with a single component input (i.e. a component of single wavelength), and thus traces t1 and t2 may be considered as representing sections S and S3 respectively of FIGURE l.

It will be noted that here the scanning is done by moving the instrument output with respect to the analog output, whereas for the system shown in FIGURE 3 the analog output was moved with respect to the instrument output. Of course either method will serve, the primary requirement being that there be relative movement between the two outputs. i

To complete the system it therefore only remains to make the intensity of trace l2 equal that of tuace t1 by cornparing the intensities of narrow center sections of each trace, and this is done by comparing the output of photoelectric cells 110 and 111 which view narrow vertical strips of surfaces A and B respectively. As the fragmentary plan view of FIGURE 4a better shows on a larger scale, the photocell 111 (and similarly photocell 110) must be shielded from direct light from source 12i2 so as to detect only the illumination of the drum surface. The difference between the outputs of the two cells 110 and 111 is amplified in direct current amplifier 109 and fed back as a signal of appropriate polarity and magnitude to light source 112 so that trace t2 is darkened or lightened as required until it is of the same intensity, ordinal extent, and `formation characteristic as trace t1. Diode D is of analogous function to diode D1 of FIF- URE 3 and is only needed if the system involves brightening of the trace above a standard level. If only brightening from zero level is involved then no diode is needed, as there cannot be negative illumination.

Decay of the photo-persistent brightness of the drum surface provides the necessary modification to the analog output (as stored) analogously with that provided in the FIGURE v3 example by the leakage resistors Ra etc. For a given inter-scan decay time which must be short in relation to the time required for the surface to lose all its brightness, the decay characteristics must be such that the percentage decay ris constant, and independent of the initial brightness. The FIGURE 4 system is thus essentially a decaying memory type of system.

If the input to the optical projector (analog device) is now viewed on an oscilloscope 108, or any other convenient form of system output display, the sweep of the oscilloscope being synchronized by sweep synchronizer 105, then the'output display will consist of a series. of peaks Y of varying amplitude, one such peak being displayed whenever there is a component of single wavelength present in the input to the speotometer.

Instead of a drum, the operation can be carried out on oscilloscope screen, if preferred.`

To accommodate the situation in which the ordinal ex-l tent and formation characteristic of trace l1 yvary with its position along the instrument output spectrum, it is of course necessary to vary trace t2 in sympathy by changing transparency 115, and this maybe done as before Vby 20` making a large number of such transparencies and interposing them in succession in the light projected onto low-l er surface B in synchronism m'th the drum rotation by means of any convenient link from sweep synchronizer. 165. t

In addition to comparing intensity directly in the manner shown, the comparison can be effected indirectly in a manner described more fully in connection with another decaying memory type of system shown in FIGURE 5 by applying the instrument output in negative form and a positive analog output to the same photo-persistent surface making the analog output brighter whenever the instrument output darkens thereby seeking to maintain the photo-persistent surface at a uniform standard level of illumination. This is thus a true single stonage, decaying memory system. v

In the systems described thus far the instrument output spectrum has essentially been one dimensional, that is there has only been one variable parameter the other variation being in magnitude rather than position. However the system may be used with equal facility for analytical instruments whose output is two-dimensional, as is shown in FIGURE 5. t

Here the instrument 262, which may be an optical projector or some other optical amplification device, has a lens system or some similar output structure represented symbolically by box 296 `from which the projector output is continuous-ly displayed on a translucent screen 20) when a slide representing a negative image of the two dimensional display to be analysed is examined in input chamber 204. On this screen a single component input, which in the present case may be defined as a point source, should appear as a small point image but due to distortion of the instrument in fact appears as a blurred image i1, whose form may be other than circular, and whose intensity decreases, often in a non-uniform manner, from the center outward. In fact, the light amplitude is increasing, since the decrease referred to is of a negative image. Accordingly the present invention must gen# erate a point image of appearance corresponding to image z', whenever there appears in the instrument output an image corresponding in appearance to image i1.

This is done by applying to the opposite surface of screen 200 a transparent or translucent phosphor coating 261, whose decay time is large compared with the time for one scanning cycle of the analog system to be described. The arrangement or characteristics both of the phosphor and the light from projector 262 are such that the phosphor is not activated by the light from projector 202. The analog device is similar to that described in connection with FIGURE 4 and consists of a light-tight housing 213 having positioned therein a positive transparency 215 projected and focussed by lenses 214 and 216, and illuminated by a light source 212 so that the analog device projects on phosphor coating 291, which is sensitive thereto, an image whose ordinal extent (inl this case its area) and lformation characteristic correspond to those of image i1, the image actually provided by the analytical instrument when presented with a point source input. Thus as before the analog output is made the same as to extent and formation characteristic with that of that section of the instrument output assocated 'with a single component input, in this case a point source image.

There thus remains the need for making the magnitude or intensity of the analog output equal and opposite to that of the instrument output, and this is done by means of photocell 211 which may be conveniently supported from the analog device housing 213 by means of an Varm 217. This photocell 211 is arranged to close to the screen 200 and is shielded from light from source light arising from the photo-persistence of the small area Y of screen directly beneath it and light transmittedthrough gation. The photocell 211 inspects a small center portion of image il, corresponding generally in area to that of image z', the ideal instrument output, and this output is fed to a difference ampliiier 209 where it is compared with a reference voltage BREF and the diierence fed via diode D (with a resistor RD between this diode and ground) to the light source 212. Thus, the comparison is effected indirectly by arranging the output of the analog device to be equal but opposite in intensity to the projected negative image corresponding to the positive output of the analytical instrument.

This means that the analog device output is brightened whenever the projected negative image of the instrument output is darkened, and the result is to seek to bring the phosphor coating 201 to a uniform level of intensity corresponding to the value of voltage BREF. lt will be necessary to make ERE-F correspond to the background brightness of the projected negative image.

With the system described thus far the output of the analog device will be identical as to ordinal extent and formation characteristic with that section of the instrument output associated with a point source input, and the intensity of the analog output will be equal but opposite to that of the projected negative image of the instrument output section relative to a given reference level. Thus the desired conditions have been met, and the input to the analog device may be viewed as before to give the system output. In the present case it is desirable to have the system output display in the same form as that of the instrument and this is done by providing a translucent or transparent screen 220 similar in size and shape to screen 200 which has applied to one surface a phosphor coating 221 similar to phosphor coating 291 applied to screen 260. A point image pro jection system comprising casing 223 provided at one end with a cover 225 in which is a pinhole, and at the other end with a light source 222, will project on to screen 220 a point image i2, corresponding generally to the ideal instrument point source image i, whenever a distorted image il appears at the instrument output. To control the intensity, light source 222 is connected to the input to the analog device, but, since, the system is arranged so that the analog input is a brightening pulse whenever the negativeprojected image of the instrument output is darkened, it may be desired to include in the connection to light source 222 a phase reverser 218 so that the system output display is darkened whenever the analog input is brightened. The position of image i2 is of course arranged to have the same position with respect to screen 229 as has image il with respect to screen 2G13, so that observer 226 will see in the correct position on screen 22? a point image i2 whenever a distorted image il appears on screen 2%.

There thus remains only the means for scanning the instrument output with the analog output, and this is done by a mechanical sweep synchronizer 295 which may have any convenient form, such as, for example, that used in the early type of television scanning system. By this scanning system the analog output is iirst moved along a narrow lateral trace 26741 of screen 260, and is then displaced downwardly and moved along a second narrow lateral trace 26%, immediately below trace 26711, the process being continued until the whole of the screen 266 has been scanned when it is repeated starting at the top of the screen. The vertical extent of each trace 297 is made to correspond to that of ideal point source image z', and hence of image i2 in the system output display, so that the entire system output is painted for one scanning cycle. This scanning system is of course analogous to the raster-producing mechanism of a television display.

As mentioned the analog output is such as to return screen 299 to a standard level of brightness corresponding to voltage BREF applied the difference amplifier 209.

When the projected negative image is allowed to fall on the screen, output variations are produced in photocell 2li, which in turn vary the intensity of light source 212 so as to compensate for the departure from the standard brightness level, so that after a number of paints the screen again reaches this standard brightness level. When this is done the negative projected image corresponding to the instrument output is almost exactly balanced by the analog image, and by displaying the analog input on a second screen a reproduction will be formed which corresponds to the true Variations of intensity with position of the object being viewed by the optical instrument.

As before, for reasons of stability, the analog device must be prevented from generating an output when a signal corresponding to negative brightness is fed in, since under these conditions the system may not always converge to a solution, and accordingly diode D and resistor RD are included to prevent, or minimize the possibility of, such a condition occurring.

As for the system shown and described in connection with FIGURE 5, positive transparency 215 in the analog device must be changed in synchronism with the position being scanned at any instant if the ordinal extent or area and formation characteristic of the analog output must be altered depending on its position on the instrument output image. These transparencies could, as before, be derived by taking photographs of the associated section of the instrument output image as a point source is applied in a large number of different positions to the instrument input. These transparencies could then be stored and scanned in sequence.

FIGURE 6 shows a further embodiment of the invention for improving the resolution of spectra that form part of existing records obtained at some time in the past from an analytical instrument (in this case a spectrometer), rather than constitute the contemporaneous output of an instrument operating in conjunction with the apparatus of the invention. This figure shows the instrument spectrum as 301 and the analog spectrum as 362. Light sensing elements 303 and 304 scan the two spectra simultaneously Viewing corresponding narrow sections as they sweep. Amplier 305 compares and senses any ditierence in illumination level, and varies the illumination of the analog spectrum by varying the brilliance of successive ones of a row of light sources 3536. These sources 3% are all continuously energised (including energisation at zero level) and the effect of sweeping along such sources with the output of the amplifier 395 is to modify such energisations, in synchronisrn with sweeping of the spectra. Each source 306 shines on the analog spectrum 3%2 with a beam having the same intensity distribution as a single input peak 307 of the instrument spectrum. At the same time each source 366 shines in a sharply defined beam on the system output display 308.

I claim:

1. Apparatus for improving the resolution of an output received from an analytical instrument in which a sharply defined input appears as a distributed instrument output, comprising (a) analog means for generating from a discrete input signal an analog output in the same distributed form as the instrument output,

(b) comparator means for comparing the magnitude of a section of the analog output with the magnitude of a corresponding section of the instrument output for sensing a difference therebetween, said sections being narrow in relation to the distributed width of said inputs,

(c) input signal generator means connected to said comparator means and sensitive to a said difference for feeding an input signal to said analog means of a value to tend to bring said analog output towards equality of magnitude with said instrument output to nullify said diierence at least in magnitude,

(d) sweep means connected to both said outputs and to said comparator means for causing said comparator means to carry out a series of successive sweeps of both said outputs,

(e) and means connected to said input signal generator means for sensing the input signals to said analog means.

2. Apparatus according to claim 1, including means for modifying all sections of said analog output between each successive sweep by an amount proportional to the dierence between each section and a respective reference level.

3. Apparatus according to claim 2, wherein the reference level for each section is the value of the instrument output for that section.

4. Apparatus according to claim 2, wherein said means for modifying comprises means for continuously decaying each section of the analog output between successive sensings of such section on successive sweeps of said comparator means.

5. Apparatus according to claim 2, wherein said modifying means comprises means for simultaneously modifying all sections of the analog output between successive sweeps of said comparator means.

6. Apparatus according to claim 1, wherein said means connected to said input signal generator means for sensing the input signals to the analog means comprises analog input storage means for receiving the signal fed from said input signal generator means to the analog means and for forming an integrated store of said signals.

7. Apparatus for improving the resolution of an output received from an analytical instrument in which a sharply defined input appears as a distributed instrument output, comprising (a) means for storing said distributed instrument out- PU'C,

(b) analog means for generating from a discrete input signal an analog output in the same distributed form as the instrument output,

(c) means for storing said analog output,

(d) comparator means for comparing the magnitude of a section of the analog output with the magnitude of a corresponding section of the instrument output for sensing a difference therebetween, said sections being narrow in relation to the distributed width of said outputs,

(e) input signal generator means connected to said comparator means and sensitive to a said difference for feeding an input signal to said analog means of a value to tend to bring the section of said analog out- -put under comparison towards equality of magnitude with the corresponding section of the instrument output to nullify said diierence at least in magnitude in respect of the sections momentarily under comparison while simultaneously modifying adjacent sections of the analog output in conformance with said distributed form.

(f) sweep means connected to -both said storing means and to said comparator means for causing said comparator means to carry out a series of successive sweeps of both said stored outputs to compare the sections of said outputs with each other in corresponding pairs, successively and repeatedly,

g) and means connected to said input signal generator means for sensing the input signals to said analog means as a measure of the instrument input.

8.Apparatus according to claim 7, including means for modifying all sections ofl said analog output between each successive sweep by an amount proportional to the difference between each section and a respective reference level.

9. Apparatus according to claim 8, wherein the reference level for each section is the value of the instrument output for that section.

l0. Apparatus according to claim 8, wherein said modifying means comprises means for continuously decaying each section of the analog output between successive sensings of such sections on successive sweeps of said comparator means.

1l. Apparatus according to claim 8, wherein said modifying means comprises means for simultaneously modifying all sections of the analog output between successive sweeps of said comparator means.

12. Apparatus according to claim 7, wherein said means connected to said input signal generator means for sensing the input signals to said analog means comprising analog input storage means for receiving the signal fed to the analog means and for forming an integrated store of such signals.

13. Apparatus according to claim 7, wherein said instrument and analog outputs are stored as a series of individual components.

14. Apparatus according to claim 7, wherein said instrument and analog outputs are each stored as a continuous spectrum.

No references cited. 

1. APPARATUS FOR IMPROVING THE RESOLUTION OF AN OUTPUT RECEIVED FROM AN ANALYTICAL INSTRUMENT IN WHICH A SHARPLY DEFINED INPUT APPEARS AS A DISTRIBUTED INSTRUMENT OUTPUT, COMPRISING (A) ANALOG MEANS FOR GENERATING FROM A DISCRETE INPUT SIGNAL AN ANALOG OUTPUT IN THE SAME DISTRIBUTED FORM AS THE INSTRUMENT OUTPUT, (B) COMPARATOR MEANS FOR COMPARING THE MAGNITUDE OF A SECTION OF THE ANALOG OUTPUT WITH THE MAGNITUDE OF A CORRESPONDING SECTION OF THE INSTRUMENT OUTPUT FOR SENSING A DIFFERENCE THEREBETWEEN, SAID SECTIONS BEING NARROW IN RELATION TO THE DISTRIBUTED WIDTH OF SAID INPUTS, (C) INPUT SIGNAL GENERATOR MEANS CONNECTED TO SAID COMPARATOR MEANS AND SENSITIVE TO A SAID DIFFERENCE FOR FEEDING AN INPUT SIGNAL TO SAID ANALOG MEANS OF A VALUE TO TEND TO BRING SAID ANALOG OUTPUT TOWARDS EQUALITY OF MAGNITUDE WITH SAID INSTRUMENT OUTPUT TO NULLIFY SAID DIFFERENCE AT LEAST IN MAGNITUDE, (D) SWEEP MEANS CONNECTED TO BOTH SAID OUTPUTS AND TO SAID COMPARATOR MEANS FOR CAUSING SAID COMPARATOR MEANS TO CARRY OUT A SERIES OF SUCCESSIVE SWEEPS OF BOTH SAID OUTPUTS, (E) AND MEANS CONNECTED TO SAID INPUT SIGNAL GENERATOR MEANS FOR SENSING THE INPUT SIGNALS TO SAID ANALOG MEANS. 